DNR News

June 24, 2013

Growing-season burns a natural ecological process in South Carolina

If you see or smell smoke near one of the S.C. Department of Natural Resources’ heritage preserves this spring and summer, it may be coming from a prescribed fire.

Prescribed burns (also called controlled burns) are generally conducted in the dormant season, mostly in late winter and very early spring. But periodic burns in the growing season can improve habitat in ways dormant season burns cannot. Growing-season burns, which are conducted after the new leaves appear in the spring, are much more effective in controlling undesirable hardwoods, and are key in restoring and maintaining the herbaceous vegetation so crucial to brood-rearing for species like bobwhite quail and wild turkey.

The herbaceous native vegetation stimulated by growing-season prescribed burns, especially bunch-grasses and legumes, provides excellent cover and insect foraging areas for turkey poults and quail chicks, and for hens of both species. About 90 percent of the diet of both young turkeys and bobwhite quail during the first few weeks after they hatch consists of insects, which provide vital protein for early development of feathers and muscle.

According to Johnny Stowe, S.C. Department of Natural Resources (DNR) wildlife biologist and heritage preserve manager and member of the South Carolina Prescribed Fire Council, the Indians were the state’s first land managers. Native Americans burned lands statewide for millennia, but lightning also was a source of landscape-level fires. The Southeastern United States has among the highest incidences of lightning strikes in North America, and most lightning strikes coincide with late spring and earlystetto mid-summer thunderstorms. Some of these strikes start fires, and of these fires, some of them are not extinguished by rainfall. Back before the landscape was intensively fragmented and before active fire suppression was necessary for public safety and to protect property, a relatively few lightning-ignited fires could burn for weeks, or even months, burning thousands of acres in a mosaic pattern sculpted by wind, topography, humidity and fuel factors. This mosaic, or patchwork pattern of micro-habitats, is ideal for many species of wildlife.

"Land managers are often leery of May-June burns because it has not been the traditional time of year to burn," Stowe said. "But that tradition may have had more to do with the convenience and ease of burning than anything else. In late winter, vegetation tends to be dead and dry, and hence to burn well, and certainly the cool weather makes it more pleasant to conduct such fieldwork. It is also a time of year when farmers and other land managers are not as tied up with planting, harvesting and other chores."

An understandable concern about destroying bird nests causes people to avoid growing-season burns, but if you look at it from a population or ecosystem level, rather than focusing on individual animals or nests, the clear benefit of these burns outweighs any loss of nests. And surprisingly, sometimes fires do not destroy the nests. An article in the April 2005 issue of "Turkey Call," the magazine of the National Wild Turkey Federation, notes that research in Mississippi on the effects of spring burns revealed that two hens continued incubation even after the area burned. In both cases, the eggs in the nests appeared to be unharmed. Plus, turkey and quail will often re-nest when they lose a nest. These and other South Carolina species evolved and adapted to handle such losses.

Another factor to consider is that late-winter burning may expose birds associated with grass-shrub vegetation, such as bobwhite quail, to unnecessary predation by hawks and owls, since many of these raptors are migrating northward through the state at that time of year. Research at Tall Timbers Research Station in Tallahassee, Fla., indicates that a combination of periodic May-June burns interspersed with late-winter burns may be best for increasing overall diversity and abundance of insects.

Another benefit of conducting some burns in spring and summer is that it provides more burning opportunities, which are frequently limited because of staff availability, unpredictable weather, and other factors. Land managers will always need to burn in the winter, but adding another season can increase the total number of acres burned.

Researchers from the School of Forest Resources at the University of Georgia compared the effects of year-old, growing season burns with year-old, dormant season burns on six understory-nesting songbird species and found that the season of burning had no effecton nesting success of four of the species. But for the other two species, namely, yellow-breasted chats and northern cardinals, nesting success was better on areas burned during the growing season. In the long term, periodic spring-summer burns would likely result in higher nesting success for many species of grassland birds.

The main benefit from May-June burns is probably the excellent hardwood control that results, according to Stowe. Once hardwoods leaf-out, they are much more likely to be injured or killed, both stems and roots, by fire. Winter burns tend to only top-kill hardwoods, and often do not even do that, but rather merely prune the lower limbs. Top-killed trees re-sprout vigorously each year, and may do so for decades.

Clemson University researchers found over a 43-year period at the Santee Experimental Forest in Berkeley County that dormant season burns yield dramatically different results than growing season burns. Their work revealed that summer burns greatly reduced, and even eliminated hardwood stems, while winter burns tended to only top-kill hardwoods—and even worse—they favored sweetgum, a fast-growing and generally undesirable species (in open woodlands) that sprouts prolifically after fire. Moreover, annual winter burns provide sprouts from top-killed hardwoods a full growing season to recover from fire, and the many surviving root systems produce larger numbers of sprouts after each fire.

While properly conducted winter burns may produce desirable grassland habitat if conducted over many years, the ever-present danger is that if a year or two is missed—as it often is because of weather or other factors—then the numerous, established hardwood root systems will then quickly produce vigorous sprouts that shade out the herbaceous fuel, turning the grassland into a hardwood thicket. Then it is even harder to get a fire to carry continuously across the stand, according to Stowe.

Conversely, if the hardwoods are killed roots-and-all by May-June burns, then missing a year or two is not nearly as crucial, since any hardwoods have to start from seed, which may not even be available on the site. This can be a very important factor, since hurricanes with resulting wind-fallen trees, droughts combined with high winds, heavy rainfall, personnel availability, or other factors often cause landowners to miss a year or two, or more, of burning. A primary management factor in maintaining ecosystem integrity is resilience, and reducing the number of hardwood stems in Southern pinelands by growing-season burns is one of the surest, and most efficient and effective ways to provide that resilience.

For landowners interested in visual aesthetics and unique ecosystems like wiregrass, growing-season burns are the way to go. Wiregrass blooms and produces viable seed best after growing season burns, and many wildflowers thrive best after such burns.

Crucial factors for many landowners interested in developing good quail habitat include cost, time required to achieve results, and number of coveys found in hunting season. Growing-season burns provide a quick and reliable way to drastically reduce the number of hardwood stems (complete kill of roots and stem, not just top-kill), and are quite inexpensive when compared to other tools such as herbicides, mechanical treatments, or decades of winter burning. At Tall Timbers, a two-year survey based on half-day hunts showed that more coveys of quail were found on summer burned plots than on winter burned plots.

Growing season burns require more expertise than dormant season burns, since with some fuels it can be difficult to get fire to carry after spring green-up, and the possibility of killing desirable trees may be greater.
Young longleaf pine seedlings and saplings should not be burned during the growing season. While the Longleaf Alliance and other researchers and land managers have dispelled the myth that young longleaf cannot be safely burned, these smaller size classes of longleaf should usually only be burned during the dormant season. Once the tender growing shoots (often called "candles") of young longleaf start elongating in the spring, they are very susceptible to fire damage. Except under certain exacting conditions, a fire-suppressed forest should also not be burned during the growing season because of heavy fuel buildup that can increase likelihood of injury to desirable trees. In areas where fire has been suppressed, it is best to first initiate dormant season burns for a few years before burning in the growing season.

Prescribed fire managers unfamiliar with burning outside winter months should consult a Registered Forester, Consulting Forester, Certified Wildlife Biologist or other professional who has experience with growing season burns.